a) Field of the Invention
This invention relates to a process for the preparation of .alpha.-tocopherol derivatives which are useful as antisterile vitamins, hyperlipidemics, blood flow increasing agents, oxygen radical scavengers, anti-cytosenility agents, antioxidants and the like.
b) Description of the Related Art
.alpha.-Tocopherol derivatives represented by the following formula (VII): ##STR2## wherein n stands for 0 or an integer of from 1 to 5 have heretofore each been prepared by condensing trimethylhydroquinone represented by the following formula (I): ##STR3## with one of the phytols represented by the following formulas: ##STR4## in accordance with a Friedel-Crafts reaction. ##STR5##
The catalyst is essential for the Friedel-Crafts reaction. Described specifically, Lewis acids such as zinc chloride, aluminum chloride, stannic chloride, ferric chloride, titanium tetrachloride and boron trifluoride-ether complex as well as combinations of Lewis acids and protonic acids such as hydrochloric acid, sulfuric acid and phosphoric acid have been used. For example, a process employing zinc chloride and a hydrogen halide is disclosed in Japanese Patent Publication No. 21835/70, a process using ferric chloride and hydrogen chloride is disclosed in Japanese Patent Application Laid-open (KOKAI) No. 14176/72; a process employing stannic chloride and hydrogen chloride is disclosed in Japanese Patent Publication No. 21712/70, and a process relying upon a boron trifluoride-ether complex is disclosed in Japanese Patent Publication No. 8821/72.
The catalysts employed in the conventional preparation processes of .alpha.-tocopherol derivatives (VII) are accompanied by the problem that they cannot be recovered and reused because they are extremely unstable to water and are decomposed or deactivated upon contact with water formed in the reactions or during washing with water. These catalysts are also accompanied by the economical drawback that they have to be used in a stoichiometrically equivalent amount relative to trimethylhydroquinone or the corresponding phytol and they account for a large percentage of the production cost despite their use as catalysts. They also involve the problem that they require a larger reactor and the disposal of greater waste. Further, it is difficult from the standpoint of environmental conservation to dispose of zinc, tin, phosphorus and the like. The conventional preparation processes are therefore not considered to be industrially suited.
The conventional catalysts employed in the preparation of the .alpha.-tocopherol derivatives (VII) involve many problems in economy, handling, waste disposal and the like as described above. It has therefore been desired to develop an industrially excellent catalyst as a substitute for such conventional catalysts.